The present invention is related to auto dial communication equipment in general and more particularly to a call progress status detector thereof for detecting a cadenced tone progress status of a telephone call in any one of a plurality of telephone networks.
When a user places a call in a dial telephone network, he or she first picks up the hand set and listens for a dial tone then dials the number. Thereafter, the user listens for a busy signal or a ring back signal, then either disconnects as a result of the busy signal or after waiting through a number of ring back signals, or the other party answers the call which constitutes a connection. The cadenced tones which the user hears on the telephone lines represent the aforementioned call progress status, i.e. dial tone, busy, ring back . . . etc. A user can listen to the present cadenced tone of the telephone line and quickly determine the status of the call being placed. However, when an electronic auto call communication device, such as a modem, for example, makes a call without user intervention, some electronic call progress status detector is needed to make the connect/disconnect decision. A detector of this type monitors the cadenced tone of the telephone line to establish whether or not it is a dial tone and then measures the on and off times or cadence of the dial tone. The measured on and off times are compared with certain prestored on and off time templates of call progress status to determine which status the cadenced tone present on the telephone line represents.
The aforementioned status detection operation appears simple on the surface until one appreciates that there is no universal one-to-one correspondence between a cadenced tone and a call progress status between most telephone networks. Rather, one-to-one correspondence is limited to a telephone network of a country and sometimes only to a given region of a country. In addition, some call progress status tones include multiple cadences which must be analyzed by electronic equipment. Accordingly, the same call progress status may be represented by different cadenced tones from country to country and some countries have the same call progress status represented by different multiple cadenced tones.
Presently, dial modems are designed to analyze the cadenced tones of a telephone network of a country or region thereof and even this analysis is limited to one elemental cadence of the tone. It is, of course, desired to have a modem which is operational in any one of a variety of telephone networks with the capability of detecting each cadenced tone, whether single or multiple, of the same call progress status.